The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

Programming SimpleTag Handlers
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servlet-specific behavior. Through these objects, a tag handler can retrieve all the other implicit
objects (request, session, and application) that are accessible from a JSP page. If the tag is nested,
a tag handler also has access to the handler (called the parent) that is associated with the
enclosing tag.
IncludingTag Handlers inWeb Applications
Tag handlers can be made available to a web application in two basic ways. The classes
implementing the tag handlers can be stored in an unpacked form in the /WEB-INF/classes/
subdirectory of the web application. Alternatively, if the library is distributed as a JAR, it is
stored in the /WEB-INF/lib/ directory of the web application.
How Is a SimpleTag Handler Invoked?
The SimpleTag interface defines the basic protocol between a simple tag handler and a JSP
page’s servlet. The JSP page’s servlet invokes the setJspContext, setParent, and attribute
setting methods before calling doStartTag.
ATag t = new ATag();
t.setJSPContext(...);
t.setParent(...);
t.setAttribute1(value1);
t.setAttribute2(value2);
...
t.setJspBody(new JspFragment(...))
t.doTag();
The following sections describe the methods that you need to develop for each type of tag
introduced in “Types of Tags” on page 227.
Tag Handlers for BasicTags
The handler for a basic tag without a body must implement the doTag method of the SimpleTag
interface. The doTag method is invoked when the end element of the tag is encountered.
The basic tag discussed in the first section, , would be implemented by the
following tag handler:
public HelloWorldSimpleTag extends SimpleTagSupport {
public void doTag() throws JspException, IOException {
getJspContext().getOut().write("Hello, world.");
}
}
The Java EE 5Tutorial • June 2010